Just noticed today that my IAT sensor is off by 43 degrees F...indicating 113 when actual is 70. As far as I can tell, my ECU (99 Avalon V6) uses the IAT input to fine tune fuel injection and my hunch is I could not tell any difference in this 43 degree error. You could probably detect something on a sophisticated scanner but not anything material. Am I wrong? I am willing to buy a new sensor but only if it would really make a difference. Thanks.
IAT Sensor
- Thread starter artbuc
- Start date
- Status
70 degrees is the outdoor temperature, the under-hood temperature should be higher than ambient....not saying 43 degrees higher but if AC is running it will be far hotter than ambient.
Does the temp go down if you take for a 15-20 min drive? It should.
Originally Posted By: KGMtech
70 degrees is the outdoor temperature, the under-hood temperature should be higher than ambient....not saying 43 degrees higher but if AC is running it will be far hotter than ambient.
Considering location of IAT and air flow, I would think IAT should be very close to ambient. I will check that the next time I do a cold start.
Edit. On second thought, I was parked and I bet a fair amount of inlet air was coming off radiator.
70 degrees is the outdoor temperature, the under-hood temperature should be higher than ambient....not saying 43 degrees higher but if AC is running it will be far hotter than ambient.
Considering location of IAT and air flow, I would think IAT should be very close to ambient. I will check that the next time I do a cold start.
Edit. On second thought, I was parked and I bet a fair amount of inlet air was coming off radiator.
Last edited:
Thanks for the responses. Does anyone know exactly what the ECU does with the IAT input?
Originally Posted By: artbuc
Thanks for the responses. Does anyone know exactly what the ECU does with the IAT input?
Well for one thing you need the inlet temperature so the mass air flow sensor signal can be compensated. The MAF is just a resistance wire so to obtain an accurate mass flow you need to know the temperature of the incoming air.
Thanks for the responses. Does anyone know exactly what the ECU does with the IAT input?
Well for one thing you need the inlet temperature so the mass air flow sensor signal can be compensated. The MAF is just a resistance wire so to obtain an accurate mass flow you need to know the temperature of the incoming air.
Originally Posted By: kschachn
Originally Posted By: artbuc
Thanks for the responses. Does anyone know exactly what the ECU does with the IAT input?
Well for one thing you need the inlet temperature so the mass air flow sensor signal can be compensated. The MAF is just a resistance wire so to obtain an accurate mass flow you need to know the temperature of the incoming air.
I could be wrong, but the hot wire MAF measures true mass flow and does not need temperature compensation. Cars equipped with MAP sensors need temperature data to determine density and mass flow rate.
Originally Posted By: artbuc
Thanks for the responses. Does anyone know exactly what the ECU does with the IAT input?
Well for one thing you need the inlet temperature so the mass air flow sensor signal can be compensated. The MAF is just a resistance wire so to obtain an accurate mass flow you need to know the temperature of the incoming air.
I could be wrong, but the hot wire MAF measures true mass flow and does not need temperature compensation. Cars equipped with MAP sensors need temperature data to determine density and mass flow rate.
Last edited:
The IAT is needed for air density calculations. Knowing flow is the the other half. On my chevy truck going down the highway the IAT is ~15 degrees higher than outside air temp. From the moment the air enters the hot under-hood plumbing it picks up heat before getting to the engine. One of the reasons a CAI works better.
A Heat Soaked IAT sensor throws the calcs off but ECU is able to ignore it.
A Heat Soaked IAT sensor throws the calcs off but ECU is able to ignore it.
On my car, Ive been into the ECM programming, and a high IAT causes it to pull a ton of ignition timing. There was another thread awhile ago where we discussed vehicles becoming sluggish after idling in traffic, for example, then given 10-15 minutes of drive time the power comes back.
Here is what the ignition timing modifier for air temperature looks like on my car in the PCM.
Code:
254F -74
160F -74
120F -30
100F 0
60F 4
-256F 10
-256F 10
I have seen IATs in the 140F region while idling in the summer. So you can look at that chart and kinda infer the amount of timing being removed.
It is likely that your vehicle is simply sucking in radiator heat. You should check the IAT while driving on the highway or after the car has sat off for 8 hours or more. I do use my IAT like a outside temp sensor sometimes in the winter. Always while driving down the road to see if its cold enough for ice.
Originally Posted By: artbuc
Originally Posted By: kschachn
Originally Posted By: artbuc
Thanks for the responses. Does anyone know exactly what the ECU does with the IAT input?
Well for one thing you need the inlet temperature so the mass air flow sensor signal can be compensated. The MAF is just a resistance wire so to obtain an accurate mass flow you need to know the temperature of the incoming air.
I could be wrong, but the hot wire MAF measures true mass flow and does not need temperature compensation. Cars equipped with MAP sensors need temperature data to determine density and mass flow rate.
Right...1 lb of air is 1 lb of air and the MAF reads that out. Correction to temp is not applicable.
Here is what the ignition timing modifier for air temperature looks like on my car in the PCM.
Code:
254F -74
160F -74
120F -30
100F 0
60F 4
-256F 10
-256F 10
I have seen IATs in the 140F region while idling in the summer. So you can look at that chart and kinda infer the amount of timing being removed.
It is likely that your vehicle is simply sucking in radiator heat. You should check the IAT while driving on the highway or after the car has sat off for 8 hours or more. I do use my IAT like a outside temp sensor sometimes in the winter. Always while driving down the road to see if its cold enough for ice.
Originally Posted By: artbuc
Originally Posted By: kschachn
Originally Posted By: artbuc
Thanks for the responses. Does anyone know exactly what the ECU does with the IAT input?
Well for one thing you need the inlet temperature so the mass air flow sensor signal can be compensated. The MAF is just a resistance wire so to obtain an accurate mass flow you need to know the temperature of the incoming air.
I could be wrong, but the hot wire MAF measures true mass flow and does not need temperature compensation. Cars equipped with MAP sensors need temperature data to determine density and mass flow rate.
Right...1 lb of air is 1 lb of air and the MAF reads that out. Correction to temp is not applicable.
Last edited:
Originally Posted By: Colt45ws
On my car, Ive been into the ECM programming, and a high IAT causes it to pull a ton of ignition timing. There was another thread awhile ago where we discussed vehicles becoming sluggish after idling in traffic, for example, then given 10-15 minutes of drive time the power comes back.
Here is what the ignition timing modifier for air temperature looks like on my car in the PCM.
Code:
254F -74
160F -74
120F -30
100F 0
60F 4
-256F 10
-256F 10
I have seen IATs in the 140F region while idling in the summer. So you can look at that chart and kinda infer the amount of timing being removed.
It is likely that your vehicle is simply sucking in radiator heat.
Your table is kinda wacky, That can't be degrees of timing, It being being Percentage doesn't make sense either. Though I understand reading "RAW" PCM/ECM modifier tables doesn't always make sense.
These are the tables for my Camaro, (HP-Tuners).....Easier to read. On the right is the IAT modifier (Airmass vs IAT = spark correction). On the left is Volumemetric Efficiency (MAP vs RPM = Airmass)
Now....There IS a multiplier for Coolant Temp that can drastically effect the IAT modifier, But it doesn't do anything unless the engine is HOT!
Let's keep in mind that "most" engines have knock sensors....So the IAT modifier is of less importance than it seems.
On my car, Ive been into the ECM programming, and a high IAT causes it to pull a ton of ignition timing. There was another thread awhile ago where we discussed vehicles becoming sluggish after idling in traffic, for example, then given 10-15 minutes of drive time the power comes back.
Here is what the ignition timing modifier for air temperature looks like on my car in the PCM.
Code:
254F -74
160F -74
120F -30
100F 0
60F 4
-256F 10
-256F 10
I have seen IATs in the 140F region while idling in the summer. So you can look at that chart and kinda infer the amount of timing being removed.
It is likely that your vehicle is simply sucking in radiator heat.
Your table is kinda wacky, That can't be degrees of timing, It being being Percentage doesn't make sense either. Though I understand reading "RAW" PCM/ECM modifier tables doesn't always make sense.
These are the tables for my Camaro, (HP-Tuners).....Easier to read. On the right is the IAT modifier (Airmass vs IAT = spark correction). On the left is Volumemetric Efficiency (MAP vs RPM = Airmass)
Now....There IS a multiplier for Coolant Temp that can drastically effect the IAT modifier, But it doesn't do anything unless the engine is HOT!
Let's keep in mind that "most" engines have knock sensors....So the IAT modifier is of less importance than it seems.
Originally Posted By: clinebarger
Originally Posted By: Colt45ws
On my car, Ive been into the ECM programming, and a high IAT causes it to pull a ton of ignition timing. There was another thread awhile ago where we discussed vehicles becoming sluggish after idling in traffic, for example, then given 10-15 minutes of drive time the power comes back.
Here is what the ignition timing modifier for air temperature looks like on my car in the PCM.
Code:
254F -74
160F -74
120F -30
100F 0
60F 4
-256F 10
-256F 10
I have seen IATs in the 140F region while idling in the summer. So you can look at that chart and kinda infer the amount of timing being removed.
It is likely that your vehicle is simply sucking in radiator heat.
Your table is kinda wacky, That can't be degrees of timing, It being being Percentage doesn't make sense either. Though I understand reading "RAW" PCM/ECM modifier tables doesn't always make sense.
These are the tables for my Camaro, (HP-Tuners).....Easier to read. On the right is the IAT modifier (Airmass vs IAT = spark correction). On the left is Volumemetric Efficiency (MAP vs RPM = Airmass)
Now....There IS a multiplier for Coolant Temp that can drastically effect the IAT modifier, But it doesn't do anything unless the engine is HOT!
Let's keep in mind that "most" engines have knock sensors....So the IAT modifier is of less importance than it seems.
Yes, it is degrees timing. It is a modifier, so as you know there are many other tables that shape total timing. IIRC, there is a clip at -50 so it can never command less than that even if all the tables add up to something below that.
Whoops! You made me go back and look, and there is a Multiplier table for this table I didnt pay attention to. Its been so long since Ive looked at the aoftware since the 2002 has been dead.... That table has load on the Y-axis and RPM on the X. So it filters this other table to come up with the true value. For idle, it looks like the correction would be about 8% of the value in this table. The most the value could be is 10% of this tables stated number.
Originally Posted By: Colt45ws
On my car, Ive been into the ECM programming, and a high IAT causes it to pull a ton of ignition timing. There was another thread awhile ago where we discussed vehicles becoming sluggish after idling in traffic, for example, then given 10-15 minutes of drive time the power comes back.
Here is what the ignition timing modifier for air temperature looks like on my car in the PCM.
Code:
254F -74
160F -74
120F -30
100F 0
60F 4
-256F 10
-256F 10
I have seen IATs in the 140F region while idling in the summer. So you can look at that chart and kinda infer the amount of timing being removed.
It is likely that your vehicle is simply sucking in radiator heat.
Your table is kinda wacky, That can't be degrees of timing, It being being Percentage doesn't make sense either. Though I understand reading "RAW" PCM/ECM modifier tables doesn't always make sense.
These are the tables for my Camaro, (HP-Tuners).....Easier to read. On the right is the IAT modifier (Airmass vs IAT = spark correction). On the left is Volumemetric Efficiency (MAP vs RPM = Airmass)
Now....There IS a multiplier for Coolant Temp that can drastically effect the IAT modifier, But it doesn't do anything unless the engine is HOT!
Let's keep in mind that "most" engines have knock sensors....So the IAT modifier is of less importance than it seems.
Yes, it is degrees timing. It is a modifier, so as you know there are many other tables that shape total timing. IIRC, there is a clip at -50 so it can never command less than that even if all the tables add up to something below that.
Whoops! You made me go back and look, and there is a Multiplier table for this table I didnt pay attention to. Its been so long since Ive looked at the aoftware since the 2002 has been dead.... That table has load on the Y-axis and RPM on the X. So it filters this other table to come up with the true value. For idle, it looks like the correction would be about 8% of the value in this table. The most the value could be is 10% of this tables stated number.
Last edited:
Thanks to all, especially clinebarger and colt for providing the great technical info. This morning, with everything equilibrated, coolant and IAT temps were both 79 F which matches exactly a known reference temperature. Surprisingly, outside air indicated only 72 F. I always thought it was spot on because it matched weather report temps exactly. Anyhow, it is obvious the high IAT temp was due to engine heat.
Last edited:
Originally Posted By: artbuc
I could be wrong, but the hot wire MAF measures true mass flow and does not need temperature compensation. Cars equipped with MAP sensors need temperature data to determine density and mass flow rate.
Here is what Denso says:
http://www.denso-am.com/products/automot.../how-they-work/
I was a little off, there are actually two temperature sensors, one is a resistor that does the compensation for the hot wire sensor. I thought it was the little IAT sensor but I guess not. Either way the mass flow value has to be compensated for temperature.
So in the Denso example the temperature compensation resistor only compensates the hot wire mass flow sensor, but the IAT sensor value is what is used by the ECU to determine fuel injection rate. The software doesn't actually read the value from the compensation resistor it is only there to cause a proportional change to the hot wire value based on air temperature.
I could be wrong, but the hot wire MAF measures true mass flow and does not need temperature compensation. Cars equipped with MAP sensors need temperature data to determine density and mass flow rate.
Here is what Denso says:
http://www.denso-am.com/products/automot.../how-they-work/
I was a little off, there are actually two temperature sensors, one is a resistor that does the compensation for the hot wire sensor. I thought it was the little IAT sensor but I guess not. Either way the mass flow value has to be compensated for temperature.
So in the Denso example the temperature compensation resistor only compensates the hot wire mass flow sensor, but the IAT sensor value is what is used by the ECU to determine fuel injection rate. The software doesn't actually read the value from the compensation resistor it is only there to cause a proportional change to the hot wire value based on air temperature.
Originally Posted By: Colt45ws
Right...1 lb of air is 1 lb of air and the MAF reads that out. Correction to temp is not applicable.
No that's not correct. As far as I know there are no direct measurement mass flow sensors on cars, there may be one but I am not aware of it. Measuring absolute mass flow is not easy, the type discussed here is inferred based on two values.
You're not correcting the mass flow rate for temperature, you're correcting the hot wire resistance value for temperature to obtain a mass flow rate.
Right...1 lb of air is 1 lb of air and the MAF reads that out. Correction to temp is not applicable.
No that's not correct. As far as I know there are no direct measurement mass flow sensors on cars, there may be one but I am not aware of it. Measuring absolute mass flow is not easy, the type discussed here is inferred based on two values.
You're not correcting the mass flow rate for temperature, you're correcting the hot wire resistance value for temperature to obtain a mass flow rate.
Originally Posted By: kschachn
No that's not correct. As far as I know there are no direct measurement mass flow sensors on cars, there may be one but I am not aware of it.
I respectfully disagree. The hot wire MAF sensor does directly measure mass flow rate of air. The intake air thermistor is there only to provide a reference temperature for the hot wire. It is not there to allow the ECU to convert volume to mass. The amount of current in the hot wire required to maintain its temperature is directly related to both air velocity (volume) and air density (temperature and pressure). It is also related to the difference between the temperature of the hot wire and the temperature of the air. That is why you need the intake air temperature reference. It is simple heat transfer mathematics.
No that's not correct. As far as I know there are no direct measurement mass flow sensors on cars, there may be one but I am not aware of it.
I respectfully disagree. The hot wire MAF sensor does directly measure mass flow rate of air. The intake air thermistor is there only to provide a reference temperature for the hot wire. It is not there to allow the ECU to convert volume to mass. The amount of current in the hot wire required to maintain its temperature is directly related to both air velocity (volume) and air density (temperature and pressure). It is also related to the difference between the temperature of the hot wire and the temperature of the air. That is why you need the intake air temperature reference. It is simple heat transfer mathematics.
FWIW even with a cold air intake system my intake air temp is still a little hotter than ambient temp.
Originally Posted By: artbuc
I respectfully disagree. The hot wire MAF sensor does directly measure mass flow rate of air. The intake air thermistor is there only to provide a reference temperature for the hot wire. It is not there to allow the ECU to convert volume to mass. The amount of current in the hot wire required to maintain its temperature is directly related to both air velocity (volume) and air density (temperature and pressure). It is also related to the difference between the temperature of the hot wire and the temperature of the air. That is why you need the intake air temperature reference. It is simple heat transfer mathematics.
As far as I know there is no known method of measuring mass of anything directly. It is always a calculation from some other measured value. Even in the ISS where you can't weigh the astronauts, their mass is calculated from momentum.
In an MAF sensor you're really measuring the air density (and volume) which is then used to calculate mass. I agree the temperature isn't used directly to calculate the mass value, but it certainly is used to calculate the density - otherwise you'd obtain a different value as the ambient temperature changed.
I respectfully disagree. The hot wire MAF sensor does directly measure mass flow rate of air. The intake air thermistor is there only to provide a reference temperature for the hot wire. It is not there to allow the ECU to convert volume to mass. The amount of current in the hot wire required to maintain its temperature is directly related to both air velocity (volume) and air density (temperature and pressure). It is also related to the difference between the temperature of the hot wire and the temperature of the air. That is why you need the intake air temperature reference. It is simple heat transfer mathematics.
As far as I know there is no known method of measuring mass of anything directly. It is always a calculation from some other measured value. Even in the ISS where you can't weigh the astronauts, their mass is calculated from momentum.
In an MAF sensor you're really measuring the air density (and volume) which is then used to calculate mass. I agree the temperature isn't used directly to calculate the mass value, but it certainly is used to calculate the density - otherwise you'd obtain a different value as the ambient temperature changed.
Originally Posted By: kschachn
Originally Posted By: artbuc
I respectfully disagree. The hot wire MAF sensor does directly measure mass flow rate of air. The intake air thermistor is there only to provide a reference temperature for the hot wire. It is not there to allow the ECU to convert volume to mass. The amount of current in the hot wire required to maintain its temperature is directly related to both air velocity (volume) and air density (temperature and pressure). It is also related to the difference between the temperature of the hot wire and the temperature of the air. That is why you need the intake air temperature reference. It is simple heat transfer mathematics.
As far as I know there is no known method of measuring mass of anything directly. It is always a calculation from some other measured value. Even in the ISS where you can't weigh the astronauts, their mass is calculated from momentum.
In an MAF sensor you're really measuring the air density (and volume) which is then used to calculate mass. I agree the temperature isn't used directly to calculate the mass value, but it certainly is used to calculate the density - otherwise you'd obtain a different value as the ambient temperature changed.
I agree a hot wire anemometer does not measure mass flow rate directly as it is a calibrated device. Check out the empirical relationships which are the basis for this technology. Air density (affected by variations in both ambient temperature and pressure) affects the film heat transfer coefficient. We will have to agree to disagree about air density being calculated from temperature. That was necessary in cars with MAP sensors but not necessary with MAF sensors. Maybe I am wrong but I am not in doubt, lol.
Originally Posted By: artbuc
I respectfully disagree. The hot wire MAF sensor does directly measure mass flow rate of air. The intake air thermistor is there only to provide a reference temperature for the hot wire. It is not there to allow the ECU to convert volume to mass. The amount of current in the hot wire required to maintain its temperature is directly related to both air velocity (volume) and air density (temperature and pressure). It is also related to the difference between the temperature of the hot wire and the temperature of the air. That is why you need the intake air temperature reference. It is simple heat transfer mathematics.
As far as I know there is no known method of measuring mass of anything directly. It is always a calculation from some other measured value. Even in the ISS where you can't weigh the astronauts, their mass is calculated from momentum.
In an MAF sensor you're really measuring the air density (and volume) which is then used to calculate mass. I agree the temperature isn't used directly to calculate the mass value, but it certainly is used to calculate the density - otherwise you'd obtain a different value as the ambient temperature changed.
I agree a hot wire anemometer does not measure mass flow rate directly as it is a calibrated device. Check out the empirical relationships which are the basis for this technology. Air density (affected by variations in both ambient temperature and pressure) affects the film heat transfer coefficient. We will have to agree to disagree about air density being calculated from temperature. That was necessary in cars with MAP sensors but not necessary with MAF sensors. Maybe I am wrong but I am not in doubt, lol.
Originally Posted By: kschachn
There are actually two temperature sensors, one is a resistor that does the compensation for the hot wire sensor. I thought it was the little IAT sensor but I guess not. Either way the mass flow value has to be compensated for temperature.
The temperature compensation resistor only compensates the hot wire mass flow sensor, but the IAT sensor value is what is used by the ECU to determine fuel injection rate. The software doesn't actually read the value from the compensation resistor it is only there to cause a proportional change to the hot wire value based on air temperature.
This is correct, The MAF output Frequency is corrected by the Thermistor internally with changes in air temp.
There are actually two temperature sensors, one is a resistor that does the compensation for the hot wire sensor. I thought it was the little IAT sensor but I guess not. Either way the mass flow value has to be compensated for temperature.
The temperature compensation resistor only compensates the hot wire mass flow sensor, but the IAT sensor value is what is used by the ECU to determine fuel injection rate. The software doesn't actually read the value from the compensation resistor it is only there to cause a proportional change to the hot wire value based on air temperature.
This is correct, The MAF output Frequency is corrected by the Thermistor internally with changes in air temp.
- Status